Furnace for manufacturing ingots or bars of metal or alloys, particularly bars of uranium carbide



A. ACCARY ETAL FURNACE FOR MANUFACTURING INGOTS OR BARS OF METAL OR ALLOYS, PARTICULARLY BARS OF URANIUM CARBIDE 7, 1964 2 Sheets-Sheet 1 Filed Dec.

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A. ACCARY ETAL FURNACE FOR MANUFACTURING INGOTS OR BARS OF METAL OR ALLOYS, PARTICULARLY BARS OF URANIUM CARBIDE 2 Sheets-Sheet 2 r-AMPLlFlER POLARIZED POLARIZED RE RELAY\I I /39 8]\ RE,LAYS\ RELAY\ 87 ask/- k. f

92 702 /0/ has -up- REVERSIBLE MOTOR RELAY g 2 INVENTOPS JE-mv 7kouvs flaw dam HTTOP/YE'YS United States Patent Claims. (l. 164-154) ABSTRACT OF THE DISCLOSURE A furnace for continuously manufacturing ingots from molten metal in an enclosure under vacuum. A bottomless crucible holding the molten metal is subjected to the heating action of an electron gun and has a vertically movable head which comprises the base of the crucible. The speed of the movement of the head is controlled by thermocouple means located in the enclosure near the crucible so as to keep the level of the molten metal in the crucible at a constant height notwithstanding the amount of granular metal, to be melted, which is added to the crucible by a supply system.

The present invention relates to furnaces for manufacturing ingots or bars of metal or alloys, particularly bars of uranium carbide and particularly to furnaces of the type comprising, in an enclosure having means for creating a suitable vacuum therein, a bottomless crucible with double walls, preferably cylindrical and diverging at its upper part, a head which is movable vertically beneath the said crucible and constituting initially the base of said latter, means for controlling the movement of said head, heating means constituted preferably by an electron gun having means for creating therein a suitable vacuum, the electron beam from said gun being directed onto the surface of the molten metal in the crucible, means for circulating a coolant fluid in the double wall of the crucible, and a system for supplying the material to be melted, in granular form.

It is an object of the invention to render the functioning of a furnace of this type automatic so as to reduce labour costs and to ensure its operation under economical conditions.

According to the invention, the means for controlling the downward movement of the movable head, which initially forms the base of the crucible, are controlled by control means sensitive to variations in the level of the molten metal in the crucible, in such a way that the said level remains constant.

According to one embodiment, the control means comprises a thermo-electrical couple located at a fixed position above the level of the molten metal in such a Way as to receive energy of an amount dependent on the distance of said level to said thermo-electrical couple.

Other characteristics of the invention will be evident from the description which follows and from an examination of the accompanying drawings which show, by way of example, one embodiment of an improved furnace according to the invention, and in which:

FIGURE 1 shows diagrammatically a sectional view of a complete furnace assembly, and

.FIGURE 2 is a diagram illustrating the control of the downward movement of the head for supporting the manufactured bar, in dependence upon the level of the molten metal in the crucible.

A furnace for manufacturing bars of uranium carbide, shown in FIGURE 1, comprises a bottomless crucible 1 with double walls cooled by a liquid 4 put into circulation 3,388,736 Patented June 18, 1968 by any known suitable means (not shown). The crucible is of cylindrical form and its upper part diverges or opens out into a conical shape. A vertically movable head 6, arranged in the crucible 1, constitutes initially the base of said latter. The vertical movement of the movable head 6 is effected by control means, for example, a screw 17 engaged in a rotatable nut forming part of a reduction assembly 16 driven by an electric motor 18, energised in any desired fashion preferably from the mains. The current supply is not shown as it will be apparent to those skilled in the art.

The means for heating the furnace are constituted by an electron gun 10, in which exists a suitable vacuum produced by a device 14, the electron beam from the gun 10 being directed onto the surface of the molten metal in the crucible 1. Systems for the electron bombardment of metal for melting purposes are Well-known in the art and therefore do not need to be more fully described here.

The raw material, in the form of granules 7 of uranium carbide, is fed into the crucible by means of a supply device, collectively shown as 8 and fitted with an outlet spout 9.

To control the speed of extraction of the formed bar at the level of the molten bath, so that said level shall remain constant, said level is detected by means of a device which comprises a thermo-electric couple.

For this purpose, in the cone of light 0 (FIGURE 2) determined by the shape of the upper part of the crucible 1, there is arranged a thermocouple 71 which consequently receives an energy which decreases as the distance be tween the said thermocouple and the surface of the metal bath in the crucible 1 increases. However the electromotive force produced by said thermocouple also depends on the temperature of the bath and on the temperature of the enclosure. Although the furnace operates at constant power level, the temperature of the bath varies in dependence upon the size of the deposit of granules 7 on its surface. In fact, if a large quantity of granules 7 falls into the crucible 1, the temperature of the bath decreases and its action on the thermocouple 71 for detecting the level will be equivalent to an action responsive to too low a position of the level of the bath in the crucible. An undesirable reduction in the speed of casting will then result under the action of the control means, if this particular method is not provided for.

In order to avoid this ditficulty, the errors due to the fluctuations of the temperature in the enclosure are compensated by arranging a second thermocouple 73 quite near the crucible 1, but outside of the cone of light 0. This second thermocouple 73 is connected in opposition to the thermocouple 71, for the purpose of limiting the effects due to the surface temperature and of compensating the variations of temperature of the enclosure.

The resultant electro-motive force, produced by the as sembly of the two thermocouples 71 and 73 is opposed to and compared with a reference voltage from a source 74 preferably provided with an adjusting potentiometer 75, in such a way that at the terminals 76, 77 of the assembly, the voltage output is nil when the level of the bath occupies a predetermined suitable average position Nm.

Levels of the bath which are too high or too low compared with two average positions result in the appearance of voltages of different polarities, at the terminals 76, 77. This voltage is applied at the input of an amplifier 78 which controls two sensitive polarised electronic relays 8-1, 82, themselves controlling three secondary relays 83, 84, suitable for determining, respectively, a minimum speed, an average speed, and a maximum speed of descent of the bar.

FIGURE 2 diagrammatically shows the reduction motor 18 for controlling the descent of the bars. It is supplied,

either by means of a moving contact 87 from the secondary relay 83 from a source of current 88 for example of 127 volts for the minimum speed, or by a working contact 91 of the secondary relay 85 from a source of voltage 92, at 220 volts for example, for the maximum speed, or finally by means of a resting or normal contact 94 of the secondary relay 84, from a source of current 96 with an adjustable value constituted for example, by a rotary transformer supplied with 220 volts, for the average speed. This average speed may be adjusted by means of a button which acts on the output voltage of the rotary transformer 96.

However, the average outflow of granules 7 varies from one casting to another, that is why acorrecting device of average speed is provided, which has as an object to adapt the said speed to the average outflow, by taking into account the time of response of the assembly.

The corrector device comprises a motor 101, known as a balancing motor, with two directions of rotation, connected mechanically to the movable element of the rotary transformer 96 by means of a friction clutch 102, so that it is still possible to use the manual control button 97. The secondary relays 83 and 85 supply the balancing motor 101 in order to make it turn, respectively, in one direction or in the other.

The common supply point 104 for the opposed coils of the balancing motor 101 is fed from a source 105 by means of a relay 106 which transforms the supply voltage of the source 105 into a series of pulses adjustable as to duration and repetition rate by using a cyclic timer, which supplies the coil of the said relay.

The operation of the assembly of the system for controlling the descent of the bar at the level of the bath is as follows:

Depending upon the height of the bath of molten metal, the assembly of the thermocouple 71 for detecting the level and of the ambient thermocouple 73, put into opposition to or compared with the regulated reference voltage 75, produces a resultant voltage which is fed to the input of an amplifier 78.

Three cases may occur:

(1) The bath may be at the chosen average level Nm. In these conditions, the resultant voltage of the two thermocouples 70, 73, compared with the reference voltage 75, feeds a zero output voltage to the terminals 76, 77 of the amplifier 78. The output voltage in the amplifier is thus also nil and neither of the two polarised relays 81, 82 is energised, so that the three secondary relays 83, 84, 85 are also in their resting positions. Only the resting or normal contact 94 of the secondary relay 84 for controlling the speed of the Working conditions is consequently closed. The motor 18 for controlling the descent of the bar is thus driven regularly at this working speed which corresponds to the regulating voltage of the rotary transfromer 96, the adjusting member of which is, for the moment, immobile. The balancing motor 101 is also immobile since the two relays 83, 85, which control it in one direction or the other, are not energised.

(2) The level of the bath may be too high, then, the voltage supplied to the inlet of the amplifier 78 is of negative polarity, so that the corresponding polarised relay 82, controlled by the amplifier, is energised and effects, on the one hand, the energisation of the average speed of secondary relay 84 and on the other hand, the energisation of the high speed secondary relay 85. The first consequence is: the motor 18 for controlling the descent of the bar 5 is no longer driven by the working voltage of the rotary transformer 96, but by the voltage of 220 volts of the source 92 by means of the closed contact 91 of the second ary relay 85, so that it turns more quickly and consequentially causes the too high level of the bath to fall. The second consequence is the supply of the balancing motor 101 by the second relay 85, in the direction which drives the control member of the rotary transformer to a higher voltage adjustment of said latter.

The position of the rotary transformer is thus corrected by pulses, for as long as the information of a too high level i of the bath lasts.

(3) The level of the bath may be too low. Then, the reverse procedure takes place, i.e. the positive voltage fed to the amplifier 18, causes the energisation of the polarised relay 81 and, consequently, the energisation of the two secondary relays 84 and 83 respectively cutting the supplying to the motor 18 for lowering the bar at the operating voltage and feeding it into the low voltage of the source 88 by means of the contact 87 of the secondary relay 83. The bar 5 thus drops less quickly and the level of the bath rises. In a similar Way, during the whole of the information of too low level, the balancing motor 101 receives pulses from the secondary relay 83, which causes a displacement of the adjusting member of the rotary transformer 96 inthe sense of a drop in voltage.

Consequently, it will be noted that apart from a positive or negative adjustment when the level is too high or too low, the arrangement brings about, in addition, an automatic stabilisation of the average speed of descent of the bar, in order that the level of the bath of molten metal may be kept constant.

When melting begins to occur, an approximately average speed is shown, by giving the adjusting member 97 of the rotary transformer the corresponding position. Since the duration of the pulses and their frequency are unchanged from one melting to another, no intervention on the part of the operator is necessary. If the average outflow of granules necessitates a different average speed of extraction, the duration of information indicating a bad position of the bath will tend to correct the extraction speed. Experience has shown that after a few oscillations, balance is achieved at the end of about 2 minutes.

In order to avoid riprapping of the bar, the adjustable reference voltage compared with or opposed to the electromotive force of the thermocouples, may also be programmed, in such a way that the level of the bath is regularly lowered during melting.

We claim:

1. A furnace for continuously manufacturing metal ingots comprising: an enclosure having means to form a vacuum therein; a bottomless crucible with a double wall supported in said enclosure; a vertically movable head mounted beneath said crucible forming the base of said crucible; means for displacing said movable head; heating means comprising an electron gun having means for forming a vacuum therein, and the beam of which is directed onto the surface of a bath of molten metal held by said crucible; a coolant fluid being circulated in the double wall of the crucible, and a system for supplying the material to be melted, in granular form, to the crucible; in which the improvement comprises; control means sensitive to variations of the level of the molten metal in said crucible to control said means for displacing said movable head so that said level remains substantially constant; said control means including a plurality of thermocouples, at least one first thermocouple being in a fixed position above said crucible inside the cone of energy radiated from said molten metal in said crucible and at least one other of said thermocouples being located near said crucible outside the cone of radiation emitting from said molten metal in said crucible.

2. The furnace of claim 1 further including a variable speed motor for actuating said means for displacing said movable head, said variable speed motor being selectively supplied by three sources of current with different voltages corresponding, respectively, to a low speed, a normal speed and a high speed; an amplifier; a plurality of relays energized by the output voltage of said amplifier for controlling said sources of current and a source of reference current; the input voltages to said amplifier being the resultant of the comparison of the electromotive force formed in said first thermocouple and of the voltage of said source of reference current.

3. The furnace of claim 2 wherein two polarized relays of opposite polarity are connected to the output of the amplifier; said relays controlling three secondary relays capable of controlling said motor at variable speeds corresponding to said three difierent voltages.

4. The furnace of claim 3, in which a first of secondary relays contains a normally closed contact which supplies said motor with the voltage of normal operating speed when there is no output voltage from the amplifier and neither of said two polarized relays is operated.

5. The furnace of claim 4 wherein the presence of a polarized output from said amplifier energizes the corresponding polarized relay to thereby open the normally closed contact of said first secondary relay and to close the secondary supply relay of one of the other of said secondary relays, according to the polarity of the output voltage from said amplifier.

6. The furnace of claim 5 further including a balancing motor rotatable in either direction for varying the voltage supplied to the motor during normal operating speed; an adjustable member mechanically connected to said balancing motor so as to selectively feed said balancing motor through a set of secondary contacts in the low speed secondary relay a set of supplementary contacts in the high sped secondary relay to thereby ensure an automatic correction to the normal operating speed.

7. The furnace of claim 6 in which said adjusting 6 member comprises a manual control button connected to the balancing motor by a releasable connection.

8. The furnace of claim 7 wherein the voltages of said reference current is adjustable.

9. The furnace of claim 8 wherein said other thermocouple provides a correcting system for variations in ambient temperature in the enclosure and is connected in opposition to said first thermocopule so that both thermocouples are compared to said source of reference voltage.

10. The furnace of claim 1 in which said other thermocouple is connected in opposition to said first thermocouple to thereby provide a correcting system for variation in ambient temperature in the enclosure.

References Cited UNITED STATES PATENTS 2,246,907 6/1941 Webster 164-155 2,746,105 5/1956 Ratclitr'e 164-155 3,101,515 8/1963 Hanks 164250 2,586,713 2/1952 Ratclifie et al. 164-155 2,682,691 7/1954 Harter 164- -66 2,709,284 5/1955 Evans et al. 164-4 J. SPENCER OVERHOLSER, Primary Examin r.

V. K. RISING, Assistant Examiner. 

